The starting point of this proposal is a number of behavioral studies of the extrastriate visual cortex: In Tupaia bilateral removal of the striate cortex leaves form vision preserved to a remarkable extent, but a removal of striate and extrastriate visual cortex combined greatly prolongs learning of simple visual tasks, and lesions of the extrastriate alone produce deficits in visual learning. In Galago there is evidence that the temporal cortex also has a role in visual learning, but the exact area has never been defined in either species. The significance of these results lies in the discovery in the cat that the ablation of the middle suprasylvian area has a profound effect on transfer of training from one to the opposite hemisphere as well as on visual learning. Just the same combination of deficits--retarded visual learning and deficits in hemispheric transfer--are found in the monkey by lesion of the inferotemporal cortex. What is the significance of this correlation between hemispheric transfer and visual learning? That is the question posed in this application. The method is first to identify precisely an extrastriate visual learning area in Tupaia and Galago, and second to study this area with behavioral tests of hemispheric transfer. Physiological and anatomical studies of the role of the commissures in the function of the extrastriate cortex are also proposed. We already know that the function of the extrastriate visual area in the cat does not depend on striate cortex, while the opposite is true of the monkey. This species difference suggests the possibility of convergent evolution and our studies of two carefully chosen species, Tupaia and Galago, are designed to explain the puzzling similarities and differences between the cat and monkey.
